Microsoft SqlServer Reporting Services only runs on Windows (Microsoft products genarally don't work that good under linux).
But there are hunderds of tools that allow you to DOWNLOAD the report and view it. Did you know that Konqueror can display HTML pages created by ASP.NET and hosted on IIS?! I know it's weird but it true.. You can write a simple 'host' application around
the Gecko or Webkit browser engines to make a kiosk like application.
Writing cross-platform applications is so 2009. Today we use the internet. Why would you limit to word processing and spreadsheets? What about presentations? Have you ever looked at Google Docs?
Don't want to write an ajax enabled website? That's fine. You can also resort to Silverlight 2 (or moonlight) as it's called under Linux.
It's supports a subset of WPF. Silverlight/Moonlight can display FlowDocuments and FixedDocuments.
But seriously, writing a spreadsheet that works cross-platform takes a few years (you might want to check SVN commit log at openoffice.org that get some timeline it you have hunders developers at your disposal).
It took Microsoft more than a year to Microsoft Office 2007 to OSX (Office 2008).
With big players on the market like Microsoft, OpenOffice (now part of Oracle), Google Docs and KOffice I serious doubt it if you can gather enough developers to writing another office like application. Most projects read end-of-life within a few months.
Be sensable a start using a webbrowser to display your product. Ajax, Silverlight and even Flash are strong recommedations. The last two have also offlien capabilities (Silverlight offline, Adobe Air). I believe Google has a toolkit for writing a offline web